Study: Whooping cough vaccination fades in 3 years

Nurse Susan Peel gives a whooping cough vaccination to a student at Inderkum High School, Monday, Sept. 19, 2011, in Sacramento, Calif. The whooping cough vaccine given to babies and toddlers loses much of its effectiveness after just three years _ a lot faster than doctors believed _ and that could help explain a recent series of outbreaks in the U.S. among children who were fully vaccinated, a study suggests. (AP Photo/Rich Pedroncelli)
— AP

Nurse Susan Peel gives a whooping cough vaccination to a student at Inderkum High School, Monday, Sept. 19, 2011, in Sacramento, Calif. The whooping cough vaccine given to babies and toddlers loses much of its effectiveness after just three years _ a lot faster than doctors believed _ and that could help explain a recent series of outbreaks in the U.S. among children who were fully vaccinated, a study suggests. (AP Photo/Rich Pedroncelli)
/ AP

An empty bottle of Tetanus, Diphthera and Pertussis, (whooping cough) vaccine sits on display at Inderkum High School, Monday, Sept. 19, 2011, in Sacramento, Calif. The whooping cough vaccine given to babies and toddlers loses much of its effectiveness after just three years _ a lot faster than doctors believed _ and that could help explain a recent series of outbreaks in the U.S. among children who were fully vaccinated, a study suggests. (AP Photo/Rich Pedroncelli)— AP

An empty bottle of Tetanus, Diphthera and Pertussis, (whooping cough) vaccine sits on display at Inderkum High School, Monday, Sept. 19, 2011, in Sacramento, Calif. The whooping cough vaccine given to babies and toddlers loses much of its effectiveness after just three years _ a lot faster than doctors believed _ and that could help explain a recent series of outbreaks in the U.S. among children who were fully vaccinated, a study suggests. (AP Photo/Rich Pedroncelli)
/ AP

Nurse Susan Peel draws whooping cough vaccination before giving an injection to a student at Inderkum High School, Monday, Sept. 19, 2011, in Sacramento, Calif. The whooping cough vaccine given to babies and toddlers loses much of its effectiveness after just three years _ a lot faster than doctors believed _ and that could help explain a recent series of outbreaks in the U.S. among children who were fully vaccinated, a study suggests. (AP Photo/Rich Pedroncelli)— AP

Nurse Susan Peel draws whooping cough vaccination before giving an injection to a student at Inderkum High School, Monday, Sept. 19, 2011, in Sacramento, Calif. The whooping cough vaccine given to babies and toddlers loses much of its effectiveness after just three years _ a lot faster than doctors believed _ and that could help explain a recent series of outbreaks in the U.S. among children who were fully vaccinated, a study suggests. (AP Photo/Rich Pedroncelli)
/ AP

ATLANTA 
The whooping cough vaccine given to babies and toddlers loses much of its effectiveness after just three years - a lot faster than doctors believed - and that could help explain a recent series of outbreaks in the U.S. among children who were fully vaccinated, a study suggests.

The study is small and preliminary, and its authors said the results need to be confirmed through more research. Nevertheless, the findings are likely to stir debate over whether children should get a booster shot earlier than now recommended.

"I was disturbed to find maybe we had a little more confidence in the vaccine than it might deserve," said the lead researcher, Dr. David Witt, chief of infectious disease at the Kaiser Permanente Medical Center in San Rafael, Calif. Witt presented his findings Monday at the American Society for Microbiology conference in Chicago.

The study was done in California, where whooping cough vaccinations are a hot-button issue. The state had a huge spike in whooping cough cases last year, during which more than 9,100 people fell ill and 10 babies died. California schools have turned away thousands of middle and high school students this fall who haven't gotten their booster shot.

Government health officials recommend that children get vaccinated against whooping cough in five doses, with the first shot at age 2 months and the final one between 4 and 6 years. Then youngsters are supposed to get a booster shot around 11 or 12. That means a gap of five to eight years.

Witt's study looked at roughly 15,000 children in Marin County, Calif., including 132 who got whooping cough last year. He found that youngsters who had gone three years or more since the last of their five original shots were as much as 20 times more likely to become infected than children who had been more recently vaccinated. The largest number of cases was in children 8 to 12 years old.

Whooping cough, or pertussis, is a highly contagious bacterial disease that in rare cases can be fatal. It leads to severe coughing that causes children to make a distinctive whooping sound as they gasp for breath.

Marin County has a reputation for anti-vaccine sentiment, and Witt said that when he started the study he expected to see the illness concentrated in unvaccinated people. But more than 80 percent of the children who developed whooping cough in Witt's study were fully vaccinated.

California health officials told doctors last year that they could give the booster to kids as young as 7 in an effort to stifle the outbreak. Federal health officials said that they are still studying the issue and that it is too soon to make that a standard practice.

At the Centers for Disease Control and Prevention, which makes recommendations on childhood shots, officials acknowledged that the vaccine's protection declines, but they said the agency's own studies show the drop-off is not as pronounced as Witt's research found.

The CDC has estimated that the risk of the disease can increase fourfold several years after vaccination, not 10 to 20 times. One reason may be differences in how a case of whooping cough is defined: Witt counted positive test results, while the CDC also requires more than a week of symptoms.